Similar piston assemblies are known in the state of the art. Published patent application WO 2015/148973 which is incorporated herein by reference as if fully set forth discloses an expandable piston assembly for a clutch pack including an apply piston, a stator, a rotor and at least one side cover fixed to the stator. The stator is fixed to the apply piston and includes a first arcuate segment and a first radial protrusion extending from the first arcuate segment and including a distal end, with the rotor being axially aligned with and rotatable relative to the stator and including a second arcuate segment extending proximate the first radial protrusion distal end and a second radial protrusion extending from the second arcuate segment and including a distal end proximate the first arcuate segment. This arrangement uses radially extending protrusions from the stator and rotor to form a pressure chamber that can be expanded via pressurized hydraulic fluid to rotate the rotor relative to the stator to expand the piston assembly. However, the known arrangements introduce fluid leakage to the clutch which reduces the efficiency of the transmission.